1. Field of the Invention
The present invention concerns a magnetic resonance apparatus of the type having a positioning unit with a marking unit connected thereto, and a movable patient bed, the position of which can be detected and changed by the positioning unit with the marking unit establishing examination regions of an examination subject.
2. Description of the Prior Art
A magnetic resonance apparatus of the above general type is known from German OS 199 47 328. An actuation device serves to establish an examination region of an examination subject who is positioned by movement of the patient bed in an imaging volume of the magnetic resonance apparatus. A disadvantage of this known apparatus is that, in the case of a subsequent examination of a second examination region, the examination subject must be moved out of the magnetic resonance apparatus again in order to establish the second examination region, and the overall duration of the examination is thereby extended.
A method for implementation of an angiography examination using a magnetic resonance apparatus is specified from U.S. Pat. No. 5,928,148 wherein a number of examination regions are examined within one measurement procedure.
A method and an apparatus for positioning of a patient in a medical diagnostic apparatus are described in European Application 1 382 300. The patient is detected by two differently positioned image acquisition devices outside of the diagnostic apparatus. The patient is thereby divided into various body regions by means of image analysis that are available as examination regions.
Since the radiation of RF power into a patient leads to a heating of the irradiated examination region, limit values must be complied with in setting the RF transmitting power in an MR apparatus. The setting for the selected examination region ensues, for example, on the basis of a model in which a geometry of the patient is approximated by a number of cylinders (thus for example one cylinder for each leg, one for the torso and arms, one for the head of the patient) and the RF transmitting power is correspondingly adapted for a selected examination region taking a specific absorption rate (SAR) into account. Differentiation is made only between adults and children. A relatively high uncertainty or imprecision results from this with regard to the maximum compatible RF transmitting power, so that for safety a substantially lower value is used for the data acquisition than the allowable value, which in turn leads to an extended measurement time.
A method for magnetic resonance imaging is known from German OS 101 50 138, in which, before the beginning of the diagnostic data acquisition values for the SAR are determined from patient data and a magnetic resonance pre-measurement. The entire body of the patient is thereby measured to determine the exact body geometry.